It has been conventional for a great while in the field of surgical orthopedics to entirely or partially replace joints that are worn, sclerotic or damaged by other diseases with prosthetic implants. In particular, the replacement of knee joints with corresponding implants, as well as the setting of artificial hip joints or hip joint parts, is presently part of the standard surgical repertoire in surgical orthopedics. Depending on the severity of the joint defect, highly different techniques and surgical methods have been developed in the past. In addition to total replacement prostheses where the joint surfaces and neighboring bone section are completely replaced with artificially formed implant parts, e.g. for a worn knee joint both in the region of the femur as well as in the region of the tibia, techniques and systems are now common in which worn joint surfaces are only partially replaced while largely retaining the natural bone substance. For example, there are implant systems in which only one of the two condyles of the tibia-side joint surface is replaced in knee joints with a partial prosthesis, the other condyle of course being left, and an artificial contact surface of the joint is only applied on the side of the part of the femur part opposite the replaced condyle surface provided with the artificial implant.
Such partial prostheses are frequently anchored in the bone with bar-shaped or otherwise-shaped extensions, such as with so-called fins. These fins, which are slightly oversized, are pressed into a corresponding recess or hollowed-out groove created in the bone material, and the fins are frequently formed with a trapezoidal cross-section. Such fastening mechanisms can however be used for other implants that are to be fixed in the bone as well as for total replacement prostheses, and not just for partial implants.
However when sparing partial replacement prostheses are implanted, care is taken to retain as much of the soft tissues, in particular the ligaments, surrounding the joint region possible and leave said tissues free of damage. Correspondingly, separation of the natural joint is minimized to reduce the stress and promote regeneration and the healing process at this location in order to retain as much of the joint stability provided by the natural soft tissue as possible. Consequently, related tools systems with which the structures must be created in damaged bones in which prosthetic parts are fixed must be designed such that said tool systems can also be inserted into small gaps and nonetheless function with sufficient precision.
Whereas earlier it was frequently left to the dexterity and manual skill of the surgeon to prepare the joint surfaces of the bones involved for the replacement of worn joint regions in a freehand manner, increasingly, technical tools have gained acceptance in the interim to render the surgeon's handwork easier, and to ensure that the required structures are securely and precisely arranged and formed.
Accordingly, various tool systems are known for removing bone material in which templates interact with reaming in order to create recesses of a given shape and depth.
Such a tool system that is used to ream out recesses of a predetermined contour is disclosed in DE 603 20 485 T2. A reamer having a reaming head provided with a radius is inserted into a guide slot in a plate-shaped template and clears out a cassette-like free space due to the provided guidance. Similarly, a system with a template guide and reamer is disclosed in DE 195 01 550 A1.
DE 60 2004 013 383 T2 discloses a system with a template and a reamer guided therein for preparing the condyle surfaces of a knee prosthesis. In the device depicted therein, the rotating shaft of the reamer runs substantially vertically upward and requires a great deal of free space so that, during surgery and the preparation phase, the femur part of the knee must be moved back a great deal, which cannot be reconciled with the aim of retaining the soft tissues of the joint, in particular the ligaments, and in this case, the cruciate ligaments in particular.
Furthermore, an implant system marketed by the U.S. company Stryker Corporation under the brand name of EIUS™ is known in the market for partial replacement of the knee, having a condyle surface to be replaced on one side and a joint surface implant which is also affixed to one side of the femur. A preparation tool is provided for this implant system in which a trapezoidal recess is formed in the condyle surface of the tibia to be treated. To accomplish this, there is a template part with a plate element that has a tubular section which is securely connected to the plate element and has a rectangular cross section which forms a tool tunnel running at an angle of approximately 45° relative to the plane of the plate. To form a trapezoidal recess, a drilling template is first inserted into this tunnel, and weakening holes are introduced into the bone material. The drilling insert is then removed, and the bone, perforated in this manner, is fully cleared with a clearing chisel, which is also introduced through the tunnel to form the recess into which the fin of the condyle implant is introduced. On one hand, the tool system has many parts, and the associated method for forming the recess is complicated. Using different tools, first the drill holes must first be introduced with different tools, and then final clearing of the recess must then be performed. This procedure takes up valuable time during the surgery and also leads to numerous parts and instruments having to be cleaned and disinfected following the operation.